Thermodynamics is the study of energy transformations, dealing with macroscopic systems rather than microscopic systems. It involves understanding how energy is exchanged in chemical reactions and physical processes.
Thermodynamics focuses on systems, surroundings, and boundaries. A system is the part of the universe we study, and the surroundings are everything else. The universe is the sum of the system and its surroundings.
Did You Know?
The first law of thermodynamics is also known as the law of conservation of energy.
Real-life Application:
Thermodynamics principles are applied in designing engines and refrigerators.
Systems in thermodynamics can be classified based on the exchange of energy and matter with the surroundings.
An open system exchanges both energy and matter with its surroundings. Example: A beaker of water exposed to the air.
A closed system exchanges energy but not matter with its surroundings. Example: A sealed flask containing water.
An isolated system does not exchange energy or matter with its surroundings. Example: A thermos flask.
NEET Tip:
Remember the types of systems as they frequently appear in NEET questions.
Internal energy (U) is the total energy contained within a system. It can change due to heat transfer or work done.
Work (w) and heat (q) are the two ways to change the internal energy of a system.
Example:
When you heat water, the energy is transferred as heat, increasing the water's internal energy.
NEET Problem-Solving Strategy:
Use the formula ΔU=q+w to calculate changes in internal energy.
The first law of thermodynamics states that energy cannot be created or destroyed, only transformed.
The first law can be expressed as: ΔU=q+w Where:
Mnemonic:
"Energy can't be created or destroyed, just moved around" to remember the essence of the first law.
Enthalpy is the heat content of a system at constant pressure. It is a state function and is given by: H=U+PV
The change in enthalpy (ΔH) for a reaction can be written as: ΔH=ΔU+PΔV
Real-life Application:
Enthalpy changes are crucial in understanding energy requirements for chemical processes in industries.
Heat capacity is the amount of heat required to raise the temperature of a substance by one degree Celsius.
Example:
Water has a high specific heat capacity, which is why it takes a long time to heat up.
Common Misconception:
Specific heat capacity is not the same as heat capacity. The former is per unit mass, while the latter is for the whole substance.
Thermochemical equations show the enthalpy changes during chemical reactions.
The standard enthalpy of formation (ΔfH0) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.
Example:
The standard enthalpy of formation of water: 2H2(g)+O2(g)→2H2O(l);ΔfH0=−285.8kJ/mol
NEET Tip:
Familiarize yourself with common thermochemical equations and their enthalpy changes.
Hess's Law states that the total enthalpy change of a reaction is the sum of the enthalpy changes of individual steps.
Hess’s Law can be used to calculate enthalpy changes for reactions that are difficult to measure directly.
Example:
To find the enthalpy change for the formation of CO from graphite and oxygen, combine the enthalpy changes of two known reactions.
NEET Problem-Solving Strategy:
Use Hess’s Law for indirect calculations of enthalpy changes in complex reactions.
The spontaneity of a process is determined by Gibbs free energy (ΔG).
ΔG=ΔH−TΔS Where:
Did You Know?
A negative ΔG indicates a spontaneous process.
Concept Connection:
Gibbs free energy connects thermodynamics with chemical kinetics and equilibrium.
Solution:
w=−PΔV=−1 atm×(5−2) L=−3 L atm
1 L atm=101.3 J
w=−3×101.3=−303.9 J